Risk Assessment of Displaced Sediment by an Extreme Event Cyclone in a Peri-Urban Zone Using Bioassays and Analytical...

Area of Science:

• Environmental Science
• Ecotoxicology
• Environmental Chemistry

Background:

• Cyclone Gabrielle caused significant flooding and sediment displacement in Hawke's Bay, New Zealand.
• Impacted areas included the Waitangi catchment, with potential contaminant sources from sewage treatment plants and industries.
• Displaced sediments posed a potential environmental risk to coastal and stream ecosystems south of Napier City.

Purpose of the Study:

• To assess the ecological risk of sediments displaced by Cyclone Gabrielle in the Waitangi catchment.
• To investigate potential contaminants and toxicity in post-disaster sediments.
• To evaluate the effectiveness of combined chemical and bioanalytical methods for post-disaster risk assessment.

Main Methods:

• Sediment samples collected along a gradient from the Waitangi Stream to the coastline.
• Bioassays including Microtox®, mussel embryo-larval development, and yeast assays (Aryl hydrocarbon receptor and Constitutive androstane receptor).
• Chemical analysis using targeted methods and automated identification and quantification system (AIQS-GC) for contaminant identification.

Main Results:

• Elutriates exhibited low toxicity in bioassays.
• Yeast assays indicated activity levels consistent with previous findings.
• Chemical analysis confirmed historical contamination by DDT (and metabolites DDE, DDD) and plant sterols.
• Detected contaminants and toxicity levels were comparable to typical agricultural soils.

Conclusions:

• The displaced sediments in the Waitangi catchment present a low ecological risk.
• Combined chemical and bioanalytical approaches effectively assessed post-disaster contamination risks.
• Findings suggest that sediments are characteristic of historical agricultural land use.